Porous materials, including metal, ceramic, glass and polymeric materials, have increasingly been used in a variety of applications, such as filtration, aeration, wicking, and implant and other biomedical devices. For example, porous polymeric materials can be used in medical devices that serve as substitute blood vessels, synthetic and intra-ocular lenses, electrodes, catheters, and extra-corporeal devices such as those that are connected to the body to assist in surgery or dialysis. Porous polymeric materials can also be used as filters for the separation of blood into component blood cells and plasma, microfilters for removal of microorganisms from blood, and coatings for ophthalnic lenses to prevent endothelial damage upon implantation. Porous materials have also been used in diagnostic devices such as lateral flow devices, flow through devices and other immunoassay devices.
It is often necessary to alter the surface properties of a porous material, since the application of porous materials is often limited by their lack of chemical functional group and/or their hydrophobic properties, which may be disadvantageous in applications such as liquid filtration, extraction, separation and immobilization of small molecules, polymers or large biomolecules. For example, proteins will often denature when placed in contact with hydrophobic materials, and hydrophobic porous materials cannot wick aqueous solutions. Contact lenses, implants, and related devices that are in intimate contact with the body must have hydrophilic surfaces that are biologically compatible.
Attempts have been made to modify porous materials, but with mixed success. For example, U.S. Pat. No. 4,250,029 discloses a method of manufacturing ionic rejection membrane by coating differently charged polyelectrolytes onto a membrane with a neutral polymer layer between two electrolytes. The patent, however, is directed to thin ion rejection membranes only.
U.S. Pat. No. 4,619,897 discloses that the physical and/or chemical properties of a plastic surface can be changed by adhering or bonding a different material to it.
U.S. Pat. No. 4,845,132 discloses a method that uses plasma and hydrophilic monomer to produce a hydrophilic porous membrane. However, the resulted polymer film deposited by this method is not stable; and hydrophilic monomer or polymers tend to leach out.
U.S. Pat. No. 5,540,837 discloses a method of producing permanent hydrophilic fluoropolymers by coating a charged polyelectrolyte complex on top of the fluoropolymer. The application of this patent, however, is limited to the fluorinated polymer membrane and the adhesion between the polyelectrolyte complex and fluorinated polymer substrate is poor due to the lack of strong interactions between the polyelectrolyte complex and the fluorinated membrane.
U.S. Pat. No. 5,695,640 discloses a method for producing a hydrophilic porous article by treating a porous article with the mixture of polyamide and calcium chloride methanol solution. However, the stability of the hydrophilicity obtained by this method is poor.
U.S. Pat. Nos. 5,700,559; 5,807,636 and 5,837,377 disclose a method of modifying the surfaces of plastics with plasma and sequential PEI solution treatment to provide the plastics with hydrophilicity. This method can allegedly provide relatively stable hydrophilic plastics. However, the wicking rate of the plastics deteriorates during the storage.
U.S. Pat. No. 5,856,246 discloses a method of surface modification of materials using water soluble polycation and long chain surfactant or alkyl-substituted polyanion to make fiber, textiles, polymer and membrane permanent hydrophobic or oleophobic. The method disclosed therein, however, is suitable only for charged materials, not for neutral polymers such as polyolefins.
U.S. Pat. Nos. 5,914,182 and 5,916,585 disclose a method for improving porous membrane's biomaterial binding properties by treating the porous membrane with a polymer surfactant solution. The polymeric surfactant binds to the support material through hydrophobic interactions. The first layer is then crosslinked by a chemical reagent. A secondary hydrophilic layer is brought to the membrane by dipping the membrane into a hydrophilic polymer solution. This hydrophilic polymer coating allegedly can improve biomolecule binding and form covalent bonds with the first layer. This method, however, only works on ultrathin membranes. Further, the binding between the polymer surfactant and the membrane support is weak because the binding force is based on hydrophobic interaction. In addition, the crosslinking reagent glutaldehyde used therein is highly toxic.
U.S. Pat. No. 6,020,175 discloses a method of producing multiple layered functional thin films (such as protein and dye) onto solid supports by immersing charged solid substrates into an admixed polymer ion-functional molecule solution having a net opposite electric charge. This step can be repeated to form multi-layered film. The patent is directed to solid non-porous materials.
U.S. Pat. No. 6,060,410 discloses a method of coating a hydrophobic polymer substrate with a nonstoichiometric polyelectrolyte complex in solution.
Thus, there is still a need for materials, especially porous materials, with controllable and stable wicking rates, low leaching rates, and/or functional groups that enhance the materials' application potential in filtration, separation, diagnostics and medical device areas. More specifically, there is a need to provide porous polymeric materials with controllable wicking rates, biomolecular binding abilities, chemical reactivities, and ionic selection abilities.